Total knee replacement prostheses are known in the art. In many instances, a specially designed jig or fixture enables the surgeon to make accurate and precise bone resections of the femoral surface in order to accept such prostheses. The ultimate goal with any total knee prosthesis is to approximate the function of the natural, healthy structures that the prosthesis is replacing. Should the prosthesis not be properly attached to the femur any misalignment could result in discomfort to the patient, gate problems, or degradation of the prosthesis.
For example, when attaching a knee prosthesis it is desirable to orient the prosthesis such that the pivot axis of the knee joint lies within a transverse plane that is generally oriented perpendicular to the mechanical axis of the femur. The mechanical axis lies along a line which intersects the femoral head and the center of the ankle. In the prior art, the mechanical axis had been determined from an inspection of a radiograph of the femur to be resected prior to, or even during the surgery. During the actual operation, the mechanical axis is determined by computing its valgus angle from the femoral shaft axis. It is then necessary to manually align any cutting guide and its fixtures with respect to the femoral shaft axis in order to achieve an optimum cut.
Often such cutting guides include a femoral intramedullary stem which is inserted through a pre-drilled passage way formed in the intercondylar notch and upwardly through the femur along the femoral shaft axis. Such femoral intramedullary stems often include a bracket which supports the distal femur cutting guide. The bracket includes a first pin which extends through the cutting guide to act as a pivot axis. A second pin is attached to the bracket so as to extend through an arcuate slot in the cutting guide. The cutting guide included pairs of opposing slots formed along its sides which are oriented so as to be perpendicular to a central axis of symmetry of the cutting guide. When the cutting guide is pivoted, such that the central axis of symmetry lay along the mechanical axis, so as to form the appropriate angle with the femoral shaft axis, the cutting guide slots are positioned to be perpendicular to the mechanical axis. The cutting guide is then locked into the predetermined angle with the femoral shaft axis, and resection of the distal femur may proceed.
Many examples of devices and methods may be found in the art for preparing the distal femur for total knee arthroplasty, such as U.S. Pat. No. 7,172,597 which discloses a provisional component for use with differently sized first and second prosthetic orthopedic components. The provisional component has a configuration that is substantially similar to the first prosthetic component and has a predefined correspondence to the second prosthetic component. The provisional component is mounted on a bone to assess the fit of the first prosthetic component. The provisional component includes a referencing element for defining a reference point on the bone if the fit of the provisional component indicates that the second prosthetic component should be used. An instrument guide is aligned with the reference point and used to properly position a surgical instrument to prepare the bone to receive the second prosthetic component. The provisional and prosthetic components may all be femoral components which have an articulating surface defining a single condylar-shaped projection.
U.S. Pat. No. RE39,301, incorporated herein by reference, discloses a method and apparatus for knee replacement surgery in which a femoral provisional component is provided which corresponds to a permanent component to be implanted in a human. It includes structures suitable for establishing the correct fit and position of such a component, prior to its implantation, in relation to the soft tissues of the knee before final resection of the anterior femoral surface. The provisional component further includes a cutting guide for anterior surface resection such that accurate cuts may be made with the provisional component in place. The method involves preparing the distal femoral surface using the femoral intramedullary canal as a constant reference point for posterior and distal cutting guides followed by locating the provisional component by means of a provisional intramedullary stem so that the relationship with the soft tissues of the knee may be accurately established.
U.S. Pat. No. 6,187,010, incorporated herein by reference, discloses bone cutting guides that appear to enable a surgeon to better gauge required resection characteristics. At least a portion of the guide is transparent, thereby enabling the user to optimize cut estimates and to visualize the resection as it is being performed. At least a portion of the outer surface of the body is shaped to interact with another bone or prosthetic element associated with a joint, thereby enabling the device to function both as a trial and as a cutting guide.
U.S. Pat. No. 5,879,393 discloses a posterior stabilized femoral trial apparatus for preparing a patient's femur to receive a posterior stabilized femoral prosthesis. The device includes a trial body with proximal and distal portions, the distal portion having an articulating surface for articulating with a patient's tibial component. A module selected from a kit fits the trial body at the proximal surface. The module includes a rasping surface that extends longitudinally. The trial body includes cutting surfaces at the posterior condyles. The module is removably attachable to the trial body at the proximal surface. During use the surgeon may resect the patient's femur in a revision case using the trial.
U.S. Pat. No. 6,575,980 discloses an instrument for shaping a femur preparatory to implantation of a knee prosthesis. A gap checking device is fixed to the distal end of the patient's femur and referenced to the epicondyles of the femur. The gap checking device includes slots through which a cutting instrument can be passed to shape the femur so that it can receive the femoral component of the prosthesis. One of the slots enables the distal femoral cut to be made. The thickness of the gap checking device is selected so that the distance between the distal femoral cut and the distal surface of the gap checking device plus the thickness of a shim resting on the cut proximal tibia surface is equal to the combined thickness of the tibial and femoral components of the prosthesis. This arrangement apparently enables balancing of the ligaments to be checked before the femoral cuts are made, but while the gap checking device is secured to the femur.
U.S. Pat. No. 5,053,037 discloses femoral instrumentation for long stem surgery, and provides a femoral drill guide with interchangeable femoral collets, a femoral reamer, and a femoral anterior/posterior cutting block with an adaptable anterior femoral ledge. This instrumentation allows all cuts to be made relative to the long stem component of a femoral prosthesis which will fit in the hole formed by the reamer with the collet and cutting block both oriented on the reamer, and all cuts made by the surgeon will be oriented relative to the long stem or spike component of the femoral prosthesis.
With many of the foregoing, except U.S. Pat. No. 6,187,010, it would be common practice to make one or more cuts with a resection guide in place, then move the guide aside in order to view the interface, to ensure that sufficient bone has been removed to facilitate the most ideal cement interface between the resected bone and implant component. This trial-and-error process not only consumes valuable time during the operation, but may lead to the removal of more bone stock than necessary to achieve fixation. During revision arthroplasty, such trial-and-error is complicated owing to the increased number of resected surfaces involved, and the need to ensure that these surfaces and the medullary stem are all properly aligned during the testing of trial implants and the attachment of the final prosthetic device. In the event of a misalignment, the surgeon may choose to use a final implant having a smaller than optimal diameter stem, for example, to take up the slack upon discovering a slight misalignment with respect to the stem and the resected surfaces. As such, none of the forgoing methods or devices have adequately provided surgeons with a way to easily locate resection guides in relation to the patient's body during orthopedic procedures, such as, total knee replacement surgery.